btrfs: reduce block group critical section in btrfs_add_reserved_bytes()

We are doing some things inside the block group's critical section that
are relevant only to the space_info: updating the space_info counters
bytes_reserved and bytes_may_use as well as trying to grant tickets
(calling btrfs_try_granting_tickets()), and this later can take some
time. So move all those updates to outside the block group's critical
section and still inside the space_info's critical section. Like this
we keep the block group's critical section only for block group updates
and can help reduce contention on a block group's lock.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 14 insertions, 6 deletions

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 856bda9c99d9..b964eacc1610 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -3813,22 +3813,26 @@ int btrfs_add_reserved_bytes(struct btrfs_block_group *cache,
 	spin_lock(&cache->lock);
 	if (cache->ro) {
 		ret = -EAGAIN;
-		goto out;
+		goto out_error;
 	}
 
 	if (btrfs_block_group_should_use_size_class(cache)) {
 		size_class = btrfs_calc_block_group_size_class(num_bytes);
 		ret = btrfs_use_block_group_size_class(cache, size_class, force_wrong_size_class);
 		if (ret)
-			goto out;
+			goto out_error;
 	}
+
 	cache->reserved += num_bytes;
-	space_info->bytes_reserved += num_bytes;
+	if (delalloc)
+		cache->delalloc_bytes += num_bytes;
+
 	trace_btrfs_space_reservation(cache->fs_info, "space_info",
 				      space_info->flags, num_bytes, 1);
+	spin_unlock(&cache->lock);
+
+	space_info->bytes_reserved += num_bytes;
 	btrfs_space_info_update_bytes_may_use(space_info, -ram_bytes);
-	if (delalloc)
-		cache->delalloc_bytes += num_bytes;
 
 	/*
 	 * Compression can use less space than we reserved, so wake tickets if
@@ -3836,7 +3840,11 @@ int btrfs_add_reserved_bytes(struct btrfs_block_group *cache,
 	 */
 	if (num_bytes < ram_bytes)
 		btrfs_try_granting_tickets(space_info);
-out:
+	spin_unlock(&space_info->lock);
+
+	return 0;
+
+out_error:
 	spin_unlock(&cache->lock);
 	spin_unlock(&space_info->lock);
 	return ret;